The present invention relates to a manufacturing method for electronic parts having a fine multi-structure and more particularly to a manufacturing method for multi-layered electronic parts such as a multilayer ceramic capacitor and a multilayer inductor.
A multilayer ceramic capacitor which is a most typical example of multi-layered electronic parts includes many stacked dielectric ceramic layers having internal electrodes which are alternately pulled out at the end face of the layered structure. At the end face of the layered structure where the internal electrodes are pulled out, external electrodes are formed.
Although many circuit parts have been miniaturized recently, there are increasing requests also for miniaturizing such a multilayer ceramic capacitor and increasing the capacity thereof. With such a background, multilayer ceramic capacitors are manufactured by stacking very thin green sheets with a thickness of 10 xcexcm or less at present. To manufacture such capacitors at a higher yield, an art for printing very thin green sheets as mentioned above and stacking them with high precision is necessary.
In this case, since ceramic green sheets are extremely thin, it is necessary to handle them with care so ass to prevent them from getting elongation and being distorted during transporting, printing, and stacking.
Conventionally, each ceramic green sheet is formed by coating ceramic slurry in a fixed thickness on a carrier film such as a polyethylene terephthalate film and drying it. With respect to each thin ceramic green sheet, a so-called xe2x80x9cframe sticking methodxe2x80x9d has been developed, which comprises forming ceramic green sheet on a carrier film as mentioned above, punching it in a predetermined size together with the carrier film, sticking it to a frame structure together with the carrier film, and then performing the subsequent printing and stacking processes.
In the frame sticking method, a ceramic green sheet formed on a carrier film is punched together with the carrier film and sticked with the periphery thereof to a tablet-shaped frame. The frame sticking method sets the frame in a printing machine, prints the electrode pattern on the green sheet, and dries it. In this case, the green sheet is positioned on the basis of the frame and printed. Thereafter, the green sheet is punched together with the carrier film within the frame and set on the compression stand of a soft-compressor. In this case, the green sheet of the lowest layer is put on the soft-compression stand with the carrier film side thereof down, and the next green sheet is loaded on it with the carrier film side thereof up, and the carrier film is torn off. This process is sequentially repeated by a predetermined number of sheets, and then the carrier film of the green sheet of the uppermost layer is left untorn off, and pressure is applied to the layered green sheets from above the carrier film as soft-compression. Thereafter, the soft-compressed layered structure is put into a mold and compressed. Thereafter, the carrier films attached to the uppermost and lowermost layers of the layered-structure are torn off and a layered structure in units of a plurality of electronic parts is completed. With respect to the green sheets stacking order in this case, needless to say, the green sheets are stacked so that, the electrode patterns are alternately pulled out at the end face of the layered structure in each layered chip capacitor.
The multi-layered structure stacked in this way is cut and divided in a chip shape for each electronic part. Furthermore, the internal electrode is exposed from the end face of each chip and each chip is barreled so as that it is hardly cracked and then calcined in a kiln. Thereafter, when an external electrode is coated and baked on each of both end faces of each calcined chip, a multilayer ceramic capacitor is completed.
However, according to the aforementioned xe2x80x9cframe sticking methodxe2x80x9d, a step of sticking a green sheet, cut together with carrier film to a frame is necessary, and in this case, operations for gluing to the frame and drying the glue are also necessary, hence troublesome steps are required. Furthermore, a problem arises that since a rack is required to fix frames to be used and the frames are expendables, the running cost is increased. In view of such defects of the conventional xe2x80x9cframe sticking methodxe2x80x9d, a green sheet printing and stacking method for printing and stacking green films by precise positioning without using frames, accordingly without performing troublesome frame sticking and an apparatus therefor are disclosed in Japanese Patent Publication 7-93231.
According to the printing and stacking method and apparatus therefor, it is possible to make a hole for positioning in a ceramic green sheet cut together with carrier film, insert a transfer head positioning pin into the positioning hole, hold the green sheet cut in the positioned state with the transfer head together with the carrier film, and to, transfer it onto the printing stand or stacking stand, transfer the green sheet to the printing stand or stacking stand together with the carrier tape by precisely positioning only by the transfer head without using tablet-shaped frames. Moreover, since each green sheet can be held and transferred by the transfer head together with the carrier tape, elongation and distortion will not be generated in the green sheet.
However, even in the printing and stacking method of the aforementioned ceramic green sheet and the apparatus therefor, a carrier film is used to form a ceramic green sheet, and a step of coating and drying ceramic slurry on each carrier film is essential, and the cost is increased. As each green sheet is made thinner, it is very difficult to tear off the sheet from the carrier film in a high quality state without causing cracking, elongation, and distortion. Furthermore, it is necessary to print the electrode layer together with the carrier film for each green sheet cut in a predetermined size and a problem inevitably arises that the loss of a printing agent for each printing is increased.
In Japanese Patent Application Laid-Open 4-500835(WO91/01346), use of a microporous sheet comprising a polyethylene polymer containing an inorganic filler as a ceramic green sheet for a multilayer ceramic capacitor is disclosed.
However, about a method for using the aforementioned microporous sheet as a ceramic green sheet and creating a layered ceramic capacitor of high quality highly efficiently from the sheet, nothing is described in the patent application and the problems on the method using carrier films are not solved at present.
An object of the present invention is to solve the problems of the prior art during manufacture of multi-layered electronic parts such as a multilayer ceramic capacitor or a multilayer inductor using ceramic sheets formed on carrier films and to provide a manufacturing method for multi-layered electronic parts of high quality for simplifying the production steps and improving the yield.
The invention is a manufacturing method for multi-layered electronic parts which is characterized in that from a roll of a polyethylene microporous sheet which has an electrode layer forming agent formed on its surface, contains 45 to 80 volume percent of inorganic filler, and has a thickness of 25 xcexcm or less, tensile strengths of 3 kg/mm2 or more in the longitudinal direction and of 1 kg/mm2 or more in the transverse direction, and an, elongation of 30% or less in the MD direction, multi-layered electronic parts are formed via (a) a step of unwinding the sheet, (b) a step of cutting the sheet in a predetermined length, (c) a step of stacking the cut sheets, and (d) a step of cutting the layered structure, and furthermore a manufacturing method for multi-layered electronic parts mentioned above wherein the method has (c) a step of compressing the layered structure between (c) the stacking step and (d) the cutting step mentioned above, and furthermore a manufacturing method for multi-layered electronic parts mentioned above wherein the method has (e) a debinder step and (f) a calcination step after (d) the cutting step mentioned above and the present invention is also multi-layered electronic parts manufactured by the aforementioned manufacturing method, especially multilayer ceramic capacitors.